In recent years, a number of semiconductor memory devices in which memory cells are arranged three-dimensionally have been proposed to increase the integration degree of memory. In such semiconductor devices, it is necessary to electrically separate memory cells or circuit elements from each other by forming a trench in a gap between memory cells or circuit elements or the like and filling the trench with an insulating material. As integration degree is increased, there is a tendency that the opening width of a trench becomes narrower and the aspect ratio of a trench (i.e., a value wherein depth of trench is divided by opening width of trench) becomes higher. Further, in a semiconductor memory device having three-dimensional structure, it is necessary for them to be crack resistance for a thicker layer when cured at a temperature of 700° C. or higher.
As such a material for filling a trench, silicon oxide has been widely and suitably used due to a high electric insulation.
As a means for filling a trench with silicon oxide, until now, silicon oxide layer had been formed on a silicon substrate having a trench, by a CVD method. However, along with recent miniaturization of semiconductor device, there is a tendency that opening width becomes narrower and aspect ratio becomes higher. For this reason, when a trench having an opening width of 0.2 μm or less and an aspect ratio of 2 or more was filled with silicon oxide by the CVD method, there was a problem that void (unfilled part) or seams (seam-like unfilled part) in the trench tended to be generated.
As a method other than the CVD method, a method has been known where microtrenchs are filled by a coating method and cured under oxidative atmosphere to form a silica layer. As a material to be used in this method, polysilazane material, polysilane material, and silicone material are known.
Among the polysilazane materials, hydrogenated polysilazane has been reported to have features such as superior trench-filling and low cure shrinkage when converted to a silicon oxide layer (see, for example, Patent Literature 1). However, hydrogenated polysilazane has a problem that a substrate tends to be easily oxidized because it requires curing by steam oxidation. Furthermore, in recent years, since there was a tendency that the width of a trench is becoming narrower and the depth of a trench is becoming deeper, there have been problems such as insufficient trench-filling, generation of cracks in a thick layer, risk of ammonia gas generated during curing.
In addition, the polysilane material had such problems that a coated polysilane compound was easily vaporized, and that a crack was generated in a thick layer (see, for example, Patent Literature 2).
The silicone material had a problem that voids or cracks were generated in an obtained silicon oxide layer because dehydration and dealcoholized condensation reaction were accompanied when coated layer was cured. Further, since great cure shrinkage was accompanied when the silicone material was converted to silicon oxide, there was a problem that density became uneven from the layer surface to the bottom.
As a method for avoiding the generation of voids and cracks using the silicone material, a composition comprising silica particles and polysiloxane compound has been proposed (see, for example, Patent Literature 3).
However, since silica particles defined as silicon oxide particles and polysiloxane compound defined as silicon atom binder in Patent Literature 3 were only mixed each other, there was such problems that pot life (storage stability at room temperature) of the solution was not sufficient, and that trench-filling for a trench having 30 nm or less opening width and 15 or more aspect ratio was not satisfactory as well as voids being generated.
A material obtained by condensation reaction of silica particles and polysiloxane compound has been described, for example, in Patent Literatures 4 to 6. However, the material described in Patent Literatures 4 to 6 is the one which was designed for use as an interlayer insulating layer or the like. Since trench-filling is not required in the use as an interlayer insulating layer, there is no description of trench-filling in these literatures.